Brennisteinsfjöll (, "Sulfur mountains") is a minor volcanic system, with crater rows and small shield volcanoes on the Reykjanes Peninsula in southwest Iceland. Geography The mountain range is located at about from Reykjavík as well as Hafnarfjörður and to the south of the cities on the Reykjanes peninsula of Southwest Iceland. Brennisteinfjöll are not high. The highest mountain is Vífilsfell with 655 m. Geology Position within Iceland’s volcano-tectonic environment In Iceland there are about 32 volcanic systems. Volcanic system means a volcano-tectonic fissure system and – very often a bigger volcano, a so-called central volcano which in most cases is a stratovolcano and may contain a caldera. Brennisteinsfjöll does not include such a central volcano. The existence of the fissure systems in Iceland is explained by its situation, located on top of the Mid-Atlantic Ridge, a divergent plate boundary. There is most probably also a magmatic hot spot under the island which stands for increased magma production. Brennisteinsfjöll is one of four (some scientists say five) volcanic systems on the big peninsula of Reykjanes in Southwest Iceland, as such the system forms part of the Reykjanes Volcanic Belt. These others are: Reykjanes volcanic system, around Gunnuhver at the tip of the peninsula, which mostly includes Svartsengi with the geothermal power station and the Blue Lagoon; to the east of the Reykjanes system is the Krýsuvík (volcanic system), including the geothermal areas around Seltún, Krýsuvík and Trölladyngja (Reykjanes) as well as lake Kleifarvatn; and to the northeast of the Brennisteinsfjöll lies the Hengill volcanic system which reaches out to the northeast over the lake Þingvallavatn to Þingvellir. These volcanic systems are arranged en echelon and in a ca. 45° angle to the direction of rifting, scientists define this as an oblique arrangement. The volcanic systems of Reykjanes, Brennisteinsfjöll included, are stretched out in northeast-southwesterly direction over the rift on the peninsula. General description of the Brennisteinsfjöll volcanic system The volcanic system of Brennisteinsfjöll is long, has a width of about and covers about . Most to the south are the Stóra Eldborg crater row and to the north Nyðri Eldborg. The volcanic system was the most productive of all the volcanic systems of the Reykjanes peninsula during the Holocene with 30-40 eruptions and around 10 since the settlement of Iceland in the 9th century. Eruptions and current situation One of the bigger lava flows of the system run south from Brennisteinsfjöll